1. Field of the Invention
The present invention relates to database technology and an information terminal unit with history management functions for searching for or acquiring data particularly from information providers, which are connected to each other via a network and configured as a distributed database system.
2. Description of the Prior Art
Conventional distributed database systems use the Internet via a plurality of information providers (servers). Most servers distributed throughout a database structure called the World Wide Web (WWW) on the Internet provide their own individual data that users on the information terminal unit end obtain when the need arises.
Servers scattered throughout this WWW are linked together to form a distributed database using a mechanism called hyperlinks. Hyperlinks use indexes called uniform resource locators (URLs), contained in one data, or location, of the database, to point to other data in the database. Users follow these indexes to semi-automatically move to other servers and obtain data from those servers.
These URLs are basically name references and do not themselves contain the essential content of the data pointed to by the hyperlinks. Therefore, the existence of a hyperlink does not necessarily guarantee the existence of the actual data to which the hyperlink points.
Further, a feature of the distributed database system on the Internet is that the processing is not consistent throughout, but rather separate and individual processing is performed for each server. In general, the processes for creating links and for preparing data are different. In such a database system, specific data corresponding to a hyperlink will not always exist even if the hyperlink has been created.
Hence, users of the database service have only been able to search or acquire data that is available at the time of use, because the servers used to provide the data service are not all consistent in processing. For example, data that could be found or acquired in the past is sometimes altered at another point in time. When this happens, a user wanting to search or acquire that past data cannot, but can now only access the current altered data.
Since this past data cannot be accessed when the need arises, the user could save data onto a local disk while the data is still accessible, when the user thinks that data might be useful in the future.
However, it is not feasible for all users to save all the data they will need, and a large memory capacity would be necessary to store all that data. Further, if a large amount of data is saved, much labor would be required to process that data, determining which data are necessary for the user.